In order to bind articles by means of, for example, a steel band strap, the binding strap is fed from a supply source, by means of a binding head which has operatively disposed therein a plurality of drive rollers, or alternatively, the binding strap may be manually fed by means of a suitable hand tool, in such a manner as to entirely encircle the articles to be bound. When the leading end portion of the binding strap completely encircles the articles to be bound and approaches a trailing end portion of the binding strap within the vicinity of the location at which the leading end portion started to encircle the articles to be bound, such that the leading and trailing end portions of the binding strap are now overlapped with respect to each other, the leading end portion of the binding strap is gripped and held while the driving rollers are then driven in their reverse mode. Consequently, the trailing end portion of the binding strap is retracted, and the encircling binding strap is tightened and tensioned about the articles being bound to a predetermined degree. At this time, the overlapped leading and trailing end portions of the binding strap are bonded to each other, after which the binding strap is severed at a location upstream of the bonded region whereby the bound article is conveyed to another station or the like for further processing, such as, for example, its ultimate destination or transportation conveyance.
A seal fitment or crimped ferrule is one type of conventionally employed means for bonding the overlapped leading and trailing end portions of the binding strap together. Japanese Patent Application Ser. No. 61-156727 discloses one example of an improved type of seal fitment or crimped ferrule. The use of such fitments or bonding means, however, requires the generation of large forces in order to develop the requisite mechanical deformation for achieving the bonding operation. Such large forces can only be generated within a binding head having a substantially large and rigid structure, and in addition, there is the likelihood that the articles being bound may be damaged by means of the seal fitment or ferrule, or the bonding structure or apparatus of the binding head.
Another conventionally known method of bonding overlapped portions of the binding strap encircled about the articles being bound comprises the use of spot welding techniques. Two examples of conventional spot-welding techniques employed in connection with the bonding together of overlapped binding strap end portions are disclosed within FIGS. 7 and 8, and in initially considering the conventional method of FIG. 7, the articles to be bound are disclosed at 3, while the encircling binding strap is disclosed at 1, the strap 1 being fed by suitable means, not shown, from a source of supply, also not shown, such that the strap 1 passes between cooperating blades of a cutting means 2. After the leading end portion 1' of the binding strap 1 has completely encircled the article 3 to be bound, and in particular, after the leading end portion 1' of the binding strap 1 has passed between cooperating jaws of a gripper 4, the forward feeding mode of the binding strap 1 is terminated, and the gripper means 4 is activated to its closed position so as to securely grip that portion of the binding strap 1 interposed therebetween. The roller drive means, not shown, which were previously utilized to feed the binding strap 1 in its forward feed mode is now actuated in its reverse driving mode so as to retract the trailing end portion 1" thereby tensioning the strap 1 about the article 3 being bound, and when the tension developed within the binding strap 1 attains a predetermined degree or value, the overlapped strap portions, comprising the leading end portion 1' and the trailing end portion 1", disposed downstream of the gripping means 4, are bonded to each other by means of a two-point spot-welding technique or operation.
More particularly, the apparatus for carrying out the spot-welding operation is seen to comprise a lower electrode plate 6 having a first polarity and including a back bar or support surface 5, plate 6 being interposed between the article 3 being bound and the underlying surface of the leading end portion 1' of the binding strap 1, and two electrode tips 7 and 8 of an opposite polarity and reciprocably mounted above the upper surface of the trailing edge portion 1" of the binding strap 1. The electrodes 7 and 8 are simultaneously lowered into engagement with the overlapped portions 1' and 1" of the binding strap 1, and upon energization thereof, the electrodes 7 and 8 perform a two-point spot-welding operation such that the overlapped portions 1' and 1" of the binding strap 1 are bonded together. Subsequently, the cutting means 2 is operated so as to sever and separate the bonded trailing edge portion 1" of the binding strap 1 from the residual supply portion of the binding strap 1.
Referring now to FIG. 8, a second conventional spot-welding operation, and apparatus for achieving the same, is disclosed, this particular process and apparatus being disclosed within West German Laid-Open Patent Publication No. 3508835. In accordance with this conventional system, the binding strap 1 is again fed from its source of supply, not shown, by means of drive rollers, also not shown, so as to completely encircle an article 3 to be bound, the trailing end portion 1" of the binding strap 1 passing between the cooperating blades of a cutting means 2 as well as between the jaws of a second gripping means 9 which is formed, in part, with a left-end portion of a back bar or support surface 5 of a lower electrode plate 6. When the leading end portion 1' of the binding strap 1 has completely encircled the article 3 being bound such that the leading end portion 1' of the binding strap 1 has passed between the jaws of the first gripper 4, the forward drive rotation of the feed rollers is terminated, and the leading end portion 1' of the binding strip 1 is gripped by means of the first gripping means 4 as a result of the jaws of the latter being activated to their closed position. The operative mode of the drive rollers, not shown, is then reversed such that the binding strap 1 is taken up, tightened, and ultimately tensioned with a high degree of tension about the article 3 being bound, whereupon the jaws of the second gripping means 9 are activated to their closed position so as to fixedly clamp the trailing end portion 1" of the binding strap 1. The cutting means 2 is then activated so as to sever and separate the trailing end portion 1" of the binding strap 1 from the residual supply portion of the binding strap 1, and subsequently, the overlapped binding strap portions 1' and 1", clamped between both gripping means 4 and 9, are bonded to each other by means of a two-point spot welding technique or operation. More particularly, the spot-welding operation is achieved by means of the use of a lower electrode plate 6 of a first polarity, and including the back bar or support surface 5, plate 6 being interposed between the article 3 being bound and the leading end portion 1' of the binding strap 1, and two electrode tips 7 and 8, of an opposite polarity, which are reciprocably disposed above the trailing end portion 1" of the binding strap 1. Upon lowered engagement of the electrodes 7 and 8 with the overlapped portions 1' and 1" of the binding strap 1, and upon energization of the electrodes, a two-point spot-welding operation is performed such that the overlapped portions 1' and 1" of the binding strap 1 are bonded to each other.
In accordance with the first conventional spot-welding operation or technique, the overlapped portions of the binding strap are bonded together by simultaneously performing spot-welding operations at the two laterally spaced locations at predetermined welding strength values depending upon, for example, the particular material comprising the strapping band, the thickness thereof, and the like. Accordingly, a large amount of electric current is required in order to simultaneously achieve the spot-welding operations at the two laterally spaced locations. In addition, the energization of the electrodes is not conducted in a continuous manner, but to the contrary, is conducted in an intermittent manner, and within a relatively short period of time. Consequently, a large-sized power installation is required in view of the control characteristics to be achieved. In addition, the simultaneous two-point spot-welding operations are conducted under high-tension conditions prevailing within the binding strap, and with a gap formed between the two overlapping end portions 1' and 1" of the binding strap 1 due to the interdisposition of the upper gripper jaw, which also forms one part of the cutting means 2, between the upper surface of the leading end portion 1' of the binding strap 1 and the lower surface of the trailing end portion 1" of the binding strap 1. Accordingly, there is a great likelihood that the welded portions of the bonded strap 1 will crack, thereby failing to assure a perfect or proper weld. Still yet further, it is often difficult to insure that both electrode tips will come into contact with the overlapped strap portions in a simultaneous manner at both laterally spaced locations. Accordingly, sparks may be generated at one or both electrode locations thereby causing the electrode tip portions to be consumed. In order to prevent such from occurring, it is often required to adjust the relative positions or relationship defined between the two electrode tips. Yet still further, since a substantially large force is required in order to properly pressurize the overlapped strap portions together by means of the electrode tips, the back bar should have a substantially large amount of strength which means that the thickness thereof must be relatively large. This of course reduces the residual tension remaining within the bonded binding strap after the back bar has been removed.
In accordance with the second conventional spot-welding technique or operation, both the leading end and trailing end portions of the binding strap are gripped by means of the grippers 4 and 9 after the binding strap has been tensioned to its desired degree. The portion of the trailing end portion of the binding strap 1 which is interposed between the two gripping means 4 and 9 is then severed at the end thereof which is disposed within the vicinity of the first gripping means 4 such that the trailing end portion 1" of the binding strap is separated from the residual supply portion thereof. Consequently, the overlapped portions 1' and 1" of the binding strap 1 are disposed within the spot-welding region under a virtually tenion-free state whereupon the spot-welding bonding of the same by means of the two-point spot welding technique is able to be performed. Accordingly, many of the problems characteristic of the prior art system and techniques disclosed in accordance with the first conventional method, other than the fact that a large amount of electrical current or power is still required, have been overcome or resolved, and good welding properties, including good welding strength, are achieved. However, it is readily seen that the required provision and disposition of two gripping means disposed at opposite ends of the back bar 5 requires a large gripping, cutting, and bonding region, as well as a large back bar per se. Removal of such large back bar 5 subsequent to completion of the spot-welding bonding operation will of course result in a considerable reduction of the residual tension maintained within the bonded binding strap thereby reducing the binding strength of the strap with respect to the article being bound. Still further, when it is desired to bind articles having a circular cross-section, such as, for example, strip coils, pipes, tubes, and the like, it is difficult to employ a large-sized back bar.